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Hierarchical Porous Patterns of n-type 6H–SiC Crystals via Photo-electrochemical Etching

Hierarchical porous patterns have been fabricated on the C face, Si face, and cross section of n-type 6H–SiC crystal via photo-electrochemical etching using HF/C2H5OH and HF/H2O2 as electrolytes. The porous layer displayed multiple and multiscale microstructures on different faces, including stalactite-like, sponge-like and dendritic porous structures on C face, echinoid micro-patterns on Si face, and columnar and keel-shaped micro-patterns on the cross section. The formation of hierarchical porous pattern is ascribed to the dynamic competition balance between the electrochemical oxidation rate and the oxide removal rate. It was found that increasing the ionic strength of the electrolyte can obviously disturb the surface morphology of the porous SiC during the photo-electrochemical etching. Possible mechanisms for selective etching were further discussed.
 
Fig. 1. SEM images of n-type 6H–SiC wafers etched in HF and C2H5OH (20.0 wt%) solution under the current density of 50 mA/cm2: (a, c and e) HF = 4.0 wt%, (b, d and f) HF = 8.0 wt%. (a, b, e and f) images are C face patterns. (c) and (d) images are cross section patterns of samples (a) and (b), respectively. Note: (a–d) the electrode was fixed on the C face, (e and f) the electrode was fixed on the Si face. 
 
Source: Journal of Materials Science & Technology

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